This claims the benefit of United Kingdom Patent Application No. 0019133.8, filed Aug. 4, 2000.
This invention relates to a locking mechanism suitable for use in office type chairs.
Office type chairs are commonly provided with various adjustment possibilities, the most common being the height of the seat, the angle of the seat portion and the rake of the seat back. This adjustment is often carried out using spring biased levers, located at one side of the seat, one for each type of adjustment. The way in which this usually operates is that, to adjust a particular feature, the lever associated with that feature is raised, or sometimes lowered, against the action of the spring to unlock the adjustment means. It is necessary to hold the lever against the action of the spring during adjustment as release of the lever will allow it to return to the locked position, thus locking the feature against further movement. Because of the nature of the device being adjusted, it is necessary to have a strong spring as it is necessary to ensure that the seat feature remains locked in use. Unlocking of the seat while in use could cause accidents.
Difficulty, arises in carrying out adjustments because of the need to hold the lever against the spring while manoeuvring the chair feature into the desired position.
The present invention seeks to avoid this problem by enabling adjustments to be made without the need for holding the lever while making adjustments.
According to the invention, there is provided a locking mechanism suitable for use with office type chairs comprising an operating lever movable between a first position in which locking takes place and a second position in which unlocking takes place, spring means for biasing the lever into said first or locking position and catch means for holding the lever in said second or unlocked position on movement of the lever into said second position, the catch means being disengageable by movement of the lever past said second or unlocking position allowing the lever to return to said first or locking position under the action of the spring means.
Preferably, the catch means comprises a cam element rotatable with the lever and having a stop surface engageable by a lock element to prevent return of the lever to its locking position, release means being provided to disengage the lock element from the stop surface on movement of the lever past the unlocking position.
The stop surface may comprise a step in the cam surface and the lock element comprises a detent engageable with the step.
The release means may comprise a slider, slidable in a circumferential slot in the cam element, the slider having a projection engageable with the detent to move the detent away from the cam element when entrained by one end of the slot during the movement of the lever past the unlocking position. The length of the slot may be such that when the lever is in its locking position and the slider is entrained by the other end of the slot, the projection of the slider is disengaged from the detent.
Alternatively, the stop surface may comprise a hook located on a surface of the cam and the lock element comprises a pin element engageable in the hook.
In this case, the release means may comprise a second pin element constrained to move with the first pin element and movable by another surface of the cam on appropriate movement of the cam to disengage the first pin element from the hook.
The cam may be provided with a recessed portion having the hook at the base thereof co operating with the first pin and an Island structure located outwards of the base and co operating with the second pin.
An exterior slider arrangement may be provided having a slider or detent engageable with a step on an outer surface of the cam in the unlocked position of the lever.